Method of manufacturing polysilicon thin film and method of manufacturing thin film transistor having the same

ABSTRACT

In a method of manufacturing a polysilicon thin film and a method of manufacturing a TFT having the thin film, a laser beam is irradiated on a portion of an amorphous silicon thin film to liquefy the portion of the amorphous silicon thin film. The amorphous silicon thin film is on a first end portion of a substrate. The liquefied silicon is crystallized to form silicon grains. The laser beam is shifted from the first end portion towards a second end portion of the substrate opposite the first end portion by an interval in a first direction. The laser beam is then irradiated onto a portion of the amorphous silicon thin film adjacent to the silicon grains to form a first polysilicon thin film. Therefore, electrical characteristics of the amorphous silicon thin film may be improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.11/234,609, filed on Sep. 23, 2005 and relies for priority upon KoreanPatent Application No. 2005-28628 filed on Apr. 6, 2005, Korean PatentApplication No. 2005-28629 filed on Apr. 6, 2005, and Korean PatentApplication No. 2005-28632 filed on Apr. 6, 2005, the contents of whichare incorporated herein by reference in their entireties.

BACKGROUND

1. Field of the Invention

The present invention relates to a method of manufacturing a polysiliconthin film and a method of manufacturing a thin film transistor (TFT)having the thin film. More particularly, the present invention relatesto a method of manufacturing a polysilicon thin film having improvedelectrical characteristics and a method of manufacturing a TFT havingthe thin film.

2. Description of the Related Art

A liquid crystal display (LCD) device includes a switching element. Theswitching element includes an amorphous silicon thin film transistor(a-Si TFT) or a polysilicon thin film transistor (poly-Si TFT). The LCDdevice having the poly-Si TFT has a faster operating speed than the LCDdevice having the a-Si TFT, thereby providing better image displayquality than the LCD device having the a-Si TFT.

The poly-Si TFT is directly formed on a substrate, or an amorphoussilicon thin film is crystallized to form the poly-Si TFT through heattreatment.

When a temperature of a glass substrate to be used for the LCD devicerises above about 600° C., the glass substrate is deformed. This avoidthis deformation, the amorphous silicon thin film is crystallized usingan excimer laser. In the excimer laser annealing (ELA) process, a laserbeam having a high energy is irradiated onto the amorphous silicon thinfilm for a period of tens of nanoseconds to crystallize the amorphoussilicon thin film so that the glass substrate is not deformed.

When the amorphous silicon thin film is treated by the ELA process,silicon atoms in the amorphous silicon thin film are rearranged in agrain form to provide the poly-Si TFT with high electrical mobility. Inthe ELA process, the amorphous silicon thin film is melted and thensolidified to form the poly-Si TFT. That is, the poly-Si TFT formedthrough the ELA process has high operating speed in a switched-on state.

However, a leakage current flows through an interface betweenpolysilicon grains in a switched-off state. That is, silicon atoms atthe interface are not securely combined with one another, causing anelectron-hole to be formed at the interface, thereby generating aleakage current.

SUMMARY

In accordance with the present invention, a method of manufacturing apolysilicon thin film having improved electrical characteristics isprovided.

In accordance with the present invention, a method of manufacturing athin film transistor (TFT) having the above-mentioned thin film is alsoprovided.

A method of manufacturing a polysilicon thin film in accordance with anembodiment of the present invention is provided as follows. A laser beamis irradiated on a first portion of an amorphous silicon thin film toliquefy the portion of the amorphous silicon thin film. The firstportion of the amorphous silicon thin film is on a first end portion ofa substrate. The liquefied silicon is crystallized to form silicongrains. The laser beam is shifted from the first end portion to a secondend portion of the substrate opposite the first end portion by aninterval in a first direction. The laser beam is then irradiated onto asecond portion of the amorphous silicon thin film adjacent to thesilicon grains to form a first polysilicon thin film.

A method of manufacturing a thin film transistor in accordance with anembodiment of the present invention is provided as follows. An amorphoussilicon thin film is formed on a substrate. A laser beam is irradiatedonto the amorphous silicon thin film to change the amorphous siliconthin film into a polysilicon thin film. The polysilicon thin film ispartially etched to form a polysilicon pattern. A first insulating layeris formed on the substrate having the polysilicon pattern to protect thepolysilicon pattern. A gate electrode is formed on the first insulatinglayer corresponding to the polysilicon pattern. A second insulatinglayer is formed on the first insulating layer and the gate electrode.The first and second insulating layers are partially etched to formcontact holes. A source electrode and a drain electrode are formed onthe second insulating layer. The source electrode is spaced apart fromthe drain electrode. The source and drain electrodes are electricallyconnected to the polysilicon pattern through the contact holes,respectively.

In accordance with the present invention, the laser beam is repetitivelyirradiated onto the substrate from the first end portion toward thesecond end portion to increase a grain size to form the poly-Si thinfilm having improved electrical characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the present invention will becomereadily apparent by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view showing a method of manufacturing apolysilicon (poly-Si) thin film in accordance with one embodiment of thepresent invention;

FIG. 2 is a plan view showing the method of manufacturing the poly-Sithin film shown in FIG. 1;

FIG. 3 is an enlarged cross-sectional view showing a portion ‘A’ shownin FIG. 1;

FIGS. 4A to 4F are cross-sectional views showing the growth of thepoly-Si shown in FIG. 2;

FIGS. 5A to 5C are plan views showing the growth of the poly-Si shown inFIG. 2;

FIG. 6 is a plan view showing a poly-Si thin film shown in FIG. 2;

FIG. 7 is a graph showing a relationship between an intensity of a laserbeam and a location;

FIG. 8 is a graph showing a portion ‘B’ of FIG. 7;

FIGS. 9A to 9C are plan views showing a growth of a poly-Si formed by amethod of manufacturing a thin film in accordance with anotherembodiment of the present invention;

FIG. 10 is a plan view showing a poly-Si thin film formed by the methodshown in FIGS. 9A to 9C;

FIG. 11 is a plan view showing a method of manufacturing a poly-Si thinfilm in accordance with another embodiment of the present invention;

FIGS. 12A to 12C are plan views showing the method shown in FIG. 11;

FIG. 13 is a plan view showing the poly-Si thin film formed by themethod shown in FIG. 11; and

FIGS. 14A to 14D are cross-sectional views showing a method ofmanufacturing a poly-Si thin film in accordance with one embodiment ofthe present invention.

DESCRIPTION OF THE EMBODIMENTS

The invention is described more fully hereinafter with reference to theaccompanying drawings, in which embodiments of the invention are shown.This invention may, however, be embodied in many different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventionto those skilled in the art. In the drawings, the size and relativesizes of layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layer,or intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated ninety degrees or at other orientations) and the spatiallyrelative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Embodiments of the invention are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention. Assuch, variations from the shapes of the illustrations as a result, forexample, of manufacturing techniques and/or tolerances, are to beexpected. Thus, embodiments of the invention should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofthe invention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 is a cross-sectional view showing a method of manufacturing apolysilicon (poly-Si) thin film in accordance with one embodiment of thepresent invention. FIG. 2 is a plan view showing the method ofmanufacturing the poly-Si thin film shown in FIG. 1. FIG. 3 is anenlarged cross-sectional view showing a portion ‘A’ shown in FIG. 1.

Referring to FIGS. 1 to 3, an apparatus for manufacturing the poly-Sithin film 140 includes a laser unit 10, an XY-stage 20 and a substrate100.

The laser unit 10 generates a laser beam 200 to intermittently irradiatethe laser beam 200 onto the substrate 100. In the method shown in FIGS.1 to 3, the laser unit 10 comprising an excimer laser that has variouscharacteristics such as short wavelength, high output, high efficiency,etc. The excimer laser may comprise an inert gas excimer laser, an inertgas halide excimer laser, a mercury halide excimer laser, an inert gasoxide excimer laser or a polyatomic excimer laser. Examples of the inertgas include Ar₂, Kr₂, Xe₂, etc. Examples of the inert gas halide includeArF, ArCl, KrF, KrCl, XeF, XeCl, etc. Examples of the mercury halideinclude HgCl, HgBr, Hgl, etc. Examples of the inert gas oxide includeArO, KrO, XeO, etc. Examples of the polyatomic material include Kr₂F,Xe₂F, etc.

A wavelength of the laser beam 200 generated from the laser unit 10 isabout 200 nm to about 400 nm. In the method shown in FIGS. 1 to 3, thewavelength of the laser beam 200 generated from the laser unit 10 isabout 250 nm to about 308 nm. A frequency of the laser beam 200 is about300 Hz to about 6,000 Hz. In the method shown in FIGS. 1 to 3, thefrequency of the laser beam 200 is about 4,000 Hz to about 6,000 Hz.

The XY-stage 20 supports the substrate 100, and repeatedly transportsthe substrate 100 in a first direction with respect to the substrate 100by a first interval. In the method shown in FIGS. 1 to 3, the XY-stage20 transports the substrate 100 from right to left, and the XY-stage 20is shifted by the first interval in a first direction substantiallyperpendicular to the second direction with respect to the substrate 100.

As the XY-stage 20 transports the substrate 100, the laser beam 200generated from the laser unit 10 is irradiated onto the substrate 100from a first end portion 102 of the substrate 100 to a second endportion 104 of the substrate 100. The second end portion 104, which isadjacent to a right side of the substrate 100, is opposite the first endportion 102, which is adjacent to a left side of the substrate 100.Alternatively, the XY-stage 20 may transport the substrate 100 from leftto right, and the XY-stage 20 may be shifted by the first interval inthe first direction.

The substrate 100 is positioned on the XY-stage 20, and comprises atransparent substrate 110, an oxide layer 120 and an amorphous silicon(a-Si) thin film 130. In the method shown in FIGS. 1 to 3, a size of thesubstrate 100 is about 470 mm×360 mm.

The transparent substrate 110 is positioned on the XY-stage 20. Thetransparent substrate 110 comprises glass or quartz to transmit light.The oxide layer 120 is provided on the transparent substrate 110, andimproves interfacial characteristics between the transparent substrate110 and the a-Si thin film 130. The a-Si thin film 130 is deposited onthe oxide layer 120 through a chemical vapor deposition (CVD) process.The a-Si thin film 130 comprises amorphous silicon.

The laser beam 200 generated from the laser 10 is irradiated onto thea-Si thin film 130 so that the a-Si thin film 130 is rapidly melted. InFIGS. 1 to 3, the a-Si thin film 130 onto which the laser beam 200 isirradiated is fully melted, while remaining portions of the a-Si thinfilm 130 onto which the laser beam 200 is not irradiated remain in asolid state. The melted a-Si thin film 130 is rapidly crystallizedthrough a solid phase crystallization to form a polysilicon (poly-Si)thin film 140.

FIGS. 4A to 4F are cross-sectional views showing a growth of the poly-Sishown in FIG. 2. In particular, FIG. 4A is a cross-sectional viewshowing a first liquefaction of a portion of the a-Si thin film.

Referring to FIG. 4A, the laser unit 10 that generates the laser beam200 is prepared on the a-Si thin film 130 that is provided on thesubstrate 100. The substrate 100 is positioned on the XY-stage 20. Thelaser beam 200 may have a beam shape such as an elliptical shape, aquadrangular shape, etc. A first width of the beam shape of the laserbeam 200 is shorter than a second width of the beam shape of the laserbeam 200. The second width of the beam shape of the laser beam 200 maybe substantially equal to a side length of the substrate 100. In FIG.4A, the first width of the beam shape of the laser beam 200 is more thantwice the width of a unit poly-Si crystal formed by each oftransportations of the substrate 100.

The laser beam 200 generated from the laser unit 10 is firstlyirradiated onto a portion of the a-Si thin film 130 adjacent to thefirst end portion 102 of the substrate to firstly liquefy the portion ofthe a-Si thin film 130, thereby forming the liquefied silicon region134. That is, a phase of the a-Si thin film 130 is changed from anamorphous solid phase to a liquid phase. The portion of the a-Si thinfilm 130 onto which the laser beam 200 is firstly irradiated is fullyliquefied. Remaining portions of the a-Si thin film 130 remain in theamorphous solid phase.

In FIG. 4A, an intensity of a unit shot of the laser beam 200 is enoughto fully liquefy the a-Si thin film 130. Alternatively, the intensity ofthe unit shot of the laser beam 200 may be smaller than that forliquefying the a-Si thin film 130, and a plurality of shots of the laserbeam 200 may be irradiated onto the portion of the a-Si thin film 130 tofully liquefy the a-Si thin film 130.

FIG. 4B is a cross-sectional view showing a crystal growth adjacent tosides of the firstly liquefied silicon region.

Referring to FIG. 4B, the firstly liquefied silicon region 134 isfirstly crystallized from the sides of the firstly liquefied siliconregion 134 through solid phase crystallization. The firstly crystallizedpoly-Si 142 adjacent to the sides that are interfaces between theremaining portion of the a-Si thin film 132 and the firstly liquefiedsilicon region 134 functions as a core of the crystal growth. That is,the remaining portion of the a-Si 132 functions as the core of thecrystal growth so that the liquefied silicon region 134 is firstlycrystallized from sides of the firstly liquefied silicon region 134 to acenter of the firstly liquefied silicon region 134 by a lateral growthwidth of about a half of the first width of the beam shape of the laserbeam 200. In FIG. 4B, the lateral growth width is about 1 μm to about 5μm. For example, the lateral growth width may be about 2 μm to about 4μm.

FIG. 4C is a cross-sectional view showing a protruding portion in thecenter of the firstly crystallized poly-Si.

Referring to FIG. 4C, when the first crystallization of the firstlyliquefied silicon region 134 is completed, the protruding portion 146 isformed on the center of the firstly crystallized poly-Si 142. Thelateral growths from the sides meet at the center of the firstlycrystallized poly-Si 142. An electrical mobility of the protrudingportion 146 is lower than remaining portion of the firstly crystallizedpoly-Si 142. In order to make the electrical mobility of the poly-Sithin film more uniform, the protruding portion 146 is removed byfollowing the processes.

FIG. 4D is a cross-sectional view showing a secondly liquefying ofanother portion of the a-Si thin film adjacent to the firstly liquefiedsilicon region.

Referring to FIG. 4D, the laser unit 10 is shifted by the first intervalfrom the first end portion 102 toward the second end portion 104. Thelaser beam 200 generated from the laser unit 10 is secondly irradiatedonto a portion of the a-Si thin film 130, a portion of the firstlycrystallized poly-Si 142 and the firstly protruding portion 146 adjacentto the first end portion 102 of the substrate 100. The irradiation bythe laser beam 200 secondly liquefies the portion of the a-Si thin film130, the portion of the firstly crystallized poly-Si 142 and the firstlyprotruding portion 146 to form the secondly liquefied silicon region134′. The portion of the a-Si thin film 130 onto which the laser beam200 is secondly irradiated is fully liquefied. The melting of thefirstly protruding portion 146 causes the surface of the firstlycrystallized poly-Si 142 to planarize, thereby eliminating theprotruding portion 146. In FIG. 4D, the first interval is more than thehalf of the width of the firstly crystallized poly-Si 132.

FIG. 4E is a cross-sectional view showing a crystal growth adjacent tosides of the secondly liquefied silicon region 134′.

Referring to FIG. 4E, the secondly liquefied silicon region 134′ issecondly crystallized from the sides of the secondly liquefied siliconregion 134′ through solid phase crystallization. The secondlycrystallized poly-Si 142′ adjacent to the sides that are interfacesbetween the remaining portion of the firstly crystallized poly-Si 142and the secondly liquefied silicon region 134′ and an interface betweenthe remaining portion of the a-Si thin film 132 and the secondlyliquefied silicon region 134′ functions as a core of the crystal growth.That is, along a first side, crystal growth is formed from the firstlycrystallized poly-Si 142 so that the secondly liquefied silicon region134′ is secondly crystallized from the interface between the remainingportion of the firstly crystallized poly-Si 142 and the secondlyliquefied silicon region 134′. Along a second side opposite the firstside, the a-Si thin film 132 functions as the core of the crystal growthso that the secondly liquefied silicon region 134′ is secondlycrystallized from the interface between the remaining portion of thea-Si thin film 132 and the secondly liquefied silicon region 134′ by alateral growth width of about a half of the first width of the beamshape of the laser beam 200.

FIG. 4F is a cross-sectional view showing a protruding portion on acenter of the secondly liquefied silicon region.

Referring to FIG. 4F, when the second crystallization of the secondlyliquefied silicon region 134′ is completed, the second protrudingportion 146′ is formed on the secondly crystallized poly-Si 142′.

The laser unit 10 is again shifted to irradiate the laser beam 200 ontoa portion of the a-Si thin film 130, a portion of the secondlycrystallized poly-Si (not shown) and the second protruding portion 146′to thirdly liquefy the portion of the a-Si thin film 130 and the portionof the secondly crystallized poly-Si 142′ to form the liquefied siliconregion 134, and eliminate the second protruding portion 146′. Theportion of the a-Si thin film 130 onto which the laser beam 200 isthirdly irradiated is fully liquefied. The above-described processes arerepeated across the surface of the substrate 100 to form the poly-Sithin film 140 having increased electrical mobility.

FIGS. 5A to 5C are plan views showing the growth of the poly-Si shown inFIG. 2. In particular, FIG. 5A is a plan view showing the poly-Si thinfilm formed by the first irradiation of the laser beam.

Referring to FIG. 5A, the laser beam 200 generated from the laser unit10 is irradiated onto the portion of the a-Si thin film 130. The portionof the a-Si thin film 130 is rapidly liquefied to form the liquefiedsilicon region 134, and crystallized from the sides of the liquefiedsilicon region 134 through the solid phase crystallization.

In the solid phase crystallization, the a-Si thin film 130 at the sidesof the liquefied silicon region 134 functions as the core of the crystalgrowth. The firstly crystallized poly-Si 142 grows from the core to forma plurality of silicon grains 143. Silicon grain boundaries 144 aredefined by adjacent silicon grains 143.

When the silicon grains 143 grow through the solid phasecrystallization, the firstly protruding portion 146 is formed on thecenter of the firstly crystallized poly-Si 142. In FIG. 5A, the firstlyprotruding portion 146 extends in the second direction.

FIG. 5B is a plan view showing the poly-Si thin film formed by thesecond irradiation of the laser beam.

Referring to FIGS. 4D and 5B, the laser unit 10 is shifted by the firstinterval D1 in the first direction from the first end portion 102 towardthe second end portion 104. The laser beam 200 generated from the laserunit 10 is secondly irradiated onto the portion of the a-Si thin film130, the portion of the firstly crystallized poly-Si 142 and the firstlyprotruding portion 146 to secondly liquefy the portion of the a-Si thinfilm 130, the portion of the firstly crystallized poly-Si 142 and thefirstly protruding portion 146 to form the secondly liquefied siliconregion, and eliminate the firstly protruding portion 146. The portion ofthe a-Si thin film 130 onto which the laser beam 200 is secondlyirradiated is fully liquefied. In FIGS. 4D and 5B, the first interval D1is no more than the half of the first width of the beam shape of thelaser beam 200, which ensures that the laser beam 200 will fully liquefythe protruding portion formed by the previous irradiation. For example,the first interval D1 of the laser beam 200 is about 1 μm to about 4 μm.

When the laser beam 200 is overly irradiated onto the a-Si thin film130, the a-Si thin film 130 separate from the oxide layer 120. In orderto prevent the separation of the a-Si thin film 130, an overlapped areabetween the firstly irradiated laser beam and the secondly irradiatedlaser beam is no more than about 90% of an area of the laser beam 200.

When the laser beam 200 generated from the laser unit 10 is secondlyirradiated onto the portion of the a-Si thin film 130, the portion ofthe firstly crystallized poly-Si 142, the portion of the a-Si thin film130, the portion of the firstly crystallized poly-Si 142 and the firstlyprotruding portion 146 are secondly liquefied to form the secondlyliquefied silicon region 134′. In addition, the firstly protrudingportion 146 is eliminated by the melting of the a-Si thin film 130. Theportion of the a-Si thin film 130 is on a right side of the laser beam200, and the portion of the firstly crystallized poly-Si 142 is on aleft side of the laser beam 200.

The secondly liquefied silicon region 134′ is secondly crystallized fromthe interface between the remaining portion of the firstly crystallizedpoly-Si 142 and the secondly liquefied silicon region 134′ so that thesilicon grains 143 grow toward a central portion of the laser beam 200.In addition, the secondly liquefied silicon region 134′ is secondlycrystallized from the interface between the remaining portion of thea-Si thin film 132 and the secondly liquefied silicon region 134′. Whenthe second crystallization of the secondly liquefied silicon region 134′is completed, the second protruding portion 146′ is formed on thesecondly crystallized poly-Si 142′ along the center of the laser beam200.

FIG. 5C is a plan view showing the poly-Si thin film formed by the thirdirradiation of the laser beam.

Referring to FIG. 5C, the laser unit 10 is shifted by a second intervalD2 in the first direction from the first end portion 102 toward thesecond end portion 104. The laser beam 200 generated from the laser unit10 is thirdly irradiated onto a portion of the a-Si thin film 130 shownin FIG. 4D, a portion of the secondly crystallized poly-Si 142′ and thesecondly protruding portion 146′ to thirdly liquefy the portion of thea-Si thin film 130 shown in FIG. 4D, the portion of the secondlycrystallized poly-Si 142′ and the secondly protruding portion 146′ toform the thirdly liquefied silicon region (not shown), and eliminate thesecondly protruding portion 146′. The portion of the a-Si thin film 130shown in FIG. 4D onto which the laser beam 200 is thirdly irradiated isfully liquefied. The second interval D2 is no more than the half of thefirst width of the beam shape of the laser beam 200. In FIG. 5C, thesecond interval D2 is substantially equal to the first interval D1.

When the laser beam 200 generated from the laser unit 10 is thirdlyirradiated onto the portion of the a-Si thin film 130 shown in FIG. 4D,the portion of the secondly crystallized poly-Si 142′, the portion ofthe a-Si thin film 130 shown in FIG. 4D, the portion of the secondlycrystallized poly-Si 142′ and the secondly protruding portion 146′ arethirdly liquefied to form the thirdly liquefied silicon region (notshown). In addition, the secondly protruding portion 146′ is eliminated.The portion of the a-Si thin film 130 shown in FIG. 4D is on a rightside of the laser beam 200, and the portion of the secondly crystallizedpoly-Si 142′ is on a left side of the laser beam 200. The thirdlyliquefied silicon region (not shown) is thirdly crystallized from theinterface between the remaining portion of the secondly crystallizedpoly-Si 142′ and the thirdly liquefied silicon region (not shown) sothat the silicon grains 143 grow toward a central portion of the laserbeam 200. In addition, the thirdly liquefied silicon region (not shown)is thirdly crystallized from the interface between the remaining portionof the a-Si thin film 132 shown in FIG. 4D and the thirdly liquefiedsilicon region (not shown). When the third crystallization of thethirdly liquefied silicon region (not shown) is completed, the thirdprotruding portion 146″ is formed on the thirdly crystallized poly-Si142″ along the center of the laser beam 200.

The generation and elimination of the protruding portions 146, 146′ and146″ are repeated so that the silicon grains 143 grow in the firstdirection across the surface of the substrate 100. Therefore, thepoly-Si thin film 140 having increased electrical mobility is formed.

FIG. 6 is a plan view showing a poly-Si thin film shown in FIG. 2.

Referring to FIG. 6, the poly-Si thin film 140 includes the silicongrains 143 and the silicon grain boundaries 144.

The silicon grains 143 extend in the first direction from a left side toa right side of the substrate. The silicon grain boundaries 144 alsoextend in a direction that is substantially in parallel with the silicongrains 143. Electrons may not flow through the silicon grain boundaries144 so that an electrical mobility of the poly-Si thin film 140 in thefirst direction is greater than an electrical mobility of the poly-Sithin film 140 in the second direction. That is, the electrons or holesmay be trapped at the silicon grain boundaries 144.

FIG. 7 is a graph showing a relationship between an energy intensity ofa laser beam and a location. The location is a horizontal length of apredetermined point on a surface on which the laser beam is irradiated.FIG. 8 is a graph showing a portion ‘B’ of FIG. 7.

Referring to FIGS. 7 and 8, an energy profile of the laser beam 200generated from the laser unit 10 includes a flat portion 220 and twoinclined portions 210. The flat portion 220 has a substantially constantenergy distribution. Each of the inclined portions 210 has an inclinedenergy distribution. The flat portion 220 is between the inclinedportions 210.

The second width of the beam shape of the laser beam 200 issubstantially equal to the side length of the substrate 100. Forexample, when the size of the substrate 100 is about 470 mm×360 mm, thesecond width of the beam shape of the laser beam 200 may be about 470 mmor about 360 mm.

When the first width L of the beam shape of the laser beam 200 isshorter than about 3 μm, the laser beam 200 may be incontrollable. Inaddition, when the first width L of the beam shape of the laser beam 200is too wide, the width of the liquefied silicon region 134 is too wideto form micro-crystals in the silicon grains. The first width L of thebeam shape of the laser beam 200 is about 3 μm to about 10 μm.

The energy intensity of the flat portion is about 400 mJ/cm² to about1,000 mJ/cm². When the energy intensity of the flat portion is less thanabout 400 mJ/cm², the laser beam 200 may be unable to liquefy the a-Sithin film 130. When the energy intensity of the flat portion is morethan about 1,000 mJ/cm², the laser beam 200 melts too large portion ofthe a-Si thin film 130 so that the a-Si thin film 130 may be separatedfrom the oxide layer 120.

An inclination S of the inclined portion is no more than about 10 μm.The inclination S of the inclined portion is no more than about 3 μm.The inclination S is a horizontal width between about 10% of the energyintensity of the flat portion 220 and about 90% of the energy intensityof the flat portion 220. The inclination S of the inclined portion 210is a ratio of the energy intensity of the laser beam 200 to a width ofthe inclined portion 210. The inclination S is determined between about10% of the energy intensity of the flat portion 220 and about 90% of theenergy intensity of the flat portion 220. A maximum energy intensity Hcorresponds to the energy intensity of the flat portion 220. When theinclination S of the inclined portion 210 is more than about 10 μm, auniformity of the energy intensity of the laser beam 200 is decreased sothat a crystal growth of the silicon grains may be deteriorated.

A variation F of the energy intensity of the flat portion 210 is no morethan about 5% of a maximum energy intensity 222 of the flat portion 210.That is, a difference between the maximum energy intensity 222 of theflat portion 210 and a minimum energy intensity 224 of the flat portion210 is no more than about 5%. When the variation F of the energyintensity is more than about 5%, the uniformity of the energy intensityof the laser beam 200 is deteriorated, and micro-crystals may remain inthe liquefied silicon region.

The laser beam 200 is repetitively irradiated onto the a-Si thin film130, and is shifted by the interval to form the poly-Si thin film 140having silicon grains 143 of increased sizes.

FIGS. 9A to 9C are plan views showing a growth of a poly-Si formed by amethod of manufacturing a thin film in accordance with anotherembodiment of the present invention. The method of manufacturing thethin film of FIGS. 9A to 9C is substantially the same as in FIGS. 1 to8, except for the poly-Si thin film. Thus, the same reference numeralswill be used to refer to the same or like parts as those described inFIGS. 1 to 8 and any further explanation concerning the above elementswill be omitted.

FIG. 9A is a plan view showing the poly-Si thin film formed by a firstirradiation of a laser beam.

Referring to FIG. 9A, the laser beam 200 generated from a laser unit 10is irradiated onto a portion of an a-Si thin film (not shown). The a-Sithin film (not shown) is provided on a substrate. The portion of thea-Si thin film (not shown) is rapidly liquefied to form a liquefiedsilicon region (not shown), and crystallized from sides of the liquefiedsilicon region (not shown) through solid phase crystallization. Theportion of the a-Si thin film (not shown) onto which the laser beam 200is firstly irradiated is fully liquefied.

In the solid phase crystallization, the a-Si thin film (not shown) atthe sides of the liquefied silicon region (not shown) functions as acore of the crystal growth. The firstly crystallized poly-Si 152 growsfrom the core to form a plurality of silicon grains 153. The silicongrain boundaries 154 are defined by adjacent silicon grains 153.

When the silicon grains 153 grow through the solid phasecrystallization, a firstly protruding portion 156 is formed on a centerof the firstly crystallized poly-Si 152. In FIG. 9A, the firstlyprotruding portion 156 extends in the second direction.

FIG. 9B is a plan view showing the poly-Si thin film formed by a secondirradiation of the laser beam.

Referring to FIG. 9B, the laser unit 10 is shifted by a third intervalB1 from a second end portion of the substrate toward a first end portionof the substrate. When the laser unit 10 is shifted in the oppositedirection to the direction of FIG. 2, sizes of the poly-Si crystals maybe uniformized, and mobility of electrons in various directions may alsobe uniformized. The laser beam 200 generated from the laser unit 10 issecondly irradiated onto a portion of the a-Si thin film (not shown) anda portion of the firstly crystallized poly-Si 152 to secondly liquefythe portion of the a-Si thin film (not shown) and the portion of thefirstly crystallized poly-Si 152 to form a secondly liquefied siliconregion (not shown). In this embodiment, the firstly protruding portion156 remains. The portion of the a-Si thin film (not shown) onto whichthe laser beam 200 is secondly irradiated is fully liquefied. In FIG.9B, the third interval B1 is more than a half of a first width of a beamshape of the laser beam 200.

When the laser beam 200 generated from the laser unit 10 is secondlyirradiated onto the portion of the a-Si thin film (not shown) and theportion of the firstly crystallized poly-Si 152, the portion of the a-Sithin film (not shown) and the portion of the firstly crystallizedpoly-Si 152 are secondly liquefied to form the secondly liquefiedsilicon region (not shown). The firstly protruding portion 156 is noteliminated. The portion of the a-Si thin film (not shown) is on one sideof the laser beam 200, and the portion of the firstly crystallizedpoly-Si 152 is on an opposite side of the laser beam 200. The one sideand the opposite side of the laser beam 200 corresponds to a left sideand a right side of the laser beam, as viewed in the perspective shownin FIG. 1.

The secondly liquefied silicon region (not shown) is secondlycrystallized from an interface between a remaining portion of thefirstly crystallized poly-Si 152 and the secondly liquefied siliconregion (not shown) so that the silicon grains 153 grow toward a centralportion of the laser beam 200. In addition, the secondly liquefiedsilicon region (not shown) is secondly crystallized from the interfacebetween the remaining portion of the a-Si thin film (not shown) and thesecondly liquefied silicon region (not shown). When the secondcrystallization of the secondly liquefied silicon region (not shown) iscompleted, the second protruding portion 156′ is formed on the secondlycrystallized poly-Si 152′ along a center of the laser beam 200. In FIG.9B, the second protruding portion 156′ is substantially in parallel withthe first protruding portion 156.

FIG. 9C is a plan view showing the poly-Si thin film formed by a thirdirradiation of the laser beam.

Referring to FIG. 9C, the laser unit 10 is shifted by a fourth intervalB2 from the second end portion toward the first end portion. The laserbeam 200 generated from the laser unit 10 is thirdly irradiated onto aportion of the a-Si thin film (not shown) and a portion of the secondlycrystallized poly-Si 152′ to thirdly liquefy the portion of the a-Sithin film (not shown) and the portion of the secondly crystallizedpoly-Si 152′. This forms a thirdly liquefied silicon region (not shown),while the secondly protruding portion 156′ remains. The fourth intervalB2 is more than the half of the first width of the beam shape of thelaser beam 200. In FIG. 9C, the fourth interval B2 is substantiallyequal to the third interval B1.

When the laser beam 200 generated from the laser unit 10 is thirdlyirradiated onto the portion of the a-Si thin film (not shown) and theportion of the secondly crystallized poly-Si 152′, the portion of thea-Si thin film (not shown) and the portion of the secondly crystallizedpoly-Si 152′ are thirdly liquefied to form a thirdly liquefied siliconregion (not shown). In addition, the secondly protruding portion 156′ isnot eliminated. The portion of the a-Si thin film (not shown) is on aleft side of the laser beam 200, and the portion of the secondlycrystallized poly-Si 152′ is on a right side of the laser beam 200, asviewed in the perspective shown in FIG. 1. The thirdly liquefied siliconregion (not shown) is thirdly crystallized from the interface betweenthe remaining portion of the secondly crystallized poly-Si 152′ and thethirdly liquefied silicon region (not shown) so that the silicon grains153 grow toward a central portion of the laser beam 200. In addition,the thirdly liquefied silicon region (not shown) is thirdly crystallizedfrom the interface between the remaining portion of the a-Si thin film(not shown) and the thirdly liquefied silicon region (not shown). Whenthe third crystallization of the thirdly liquefied silicon region (notshown) is completed, the third protruding portion 156″ is formed on thethirdly crystallized poly-Si 152″ along the center of the laser beam200. In FIG. 9C, the first, second and third protruding portions 156,156′ and 156″ are substantially in parallel with one another.

The laser unit 10 is shifted by the interval that is greater than thehalf of the first width of the beam shape of the laser beam 200 so thatthe protruding portions 156, 156′ and 156″ are not liquefied insubsequent irradiation steps. Accordingly, the protruding portions 156,156′ and 156″ are not eliminated. Therefore, a manufacturing time of thepoly-Si thin film 150 is decreased.

FIG. 10 is a plan view showing a poly-Si thin film formed by the methodshown in FIGS. 9A to 9C.

Referring to FIG. 10, the poly-Si thin film 150 includes the silicongrains 153, the silicon grain boundaries 154 and the protruding portions156, 156′ and 156″ shown in FIGS. 9A to 9C.

The protruding portions 156, 156′ and 156″ shown in FIGS. 9A to 9C aresubstantially in parallel with one another. The silicon grains 153extend between the protruding portions 156, 156′ and 156″ shown in FIGS.9A to 9C. Generally, the silicon grain boundaries 154 are inclined withrespect to the protruding portions 156, 156′ and 156″. In addition, thesilicon grains 153 are also formed adjacent to sides of the poly-Si thinfilm 150.

The poly-Si thin film 150 including the protruding portions 156, 156′and 156″ provider lower electrical mobility than a poly-Si thin filmwithout protruding portions. The poly-Si thin film 150 having lowelectrical mobility can be used for a P-channel metal oxidesemiconductor (PMOS) element.

FIG. 11 is a plan view showing a method of manufacturing a poly-Si thinfilm in accordance with another embodiment of the present invention. Themethod of manufacturing the thin film of FIG. 11 is substantially thesame as in FIGS. 1 to 8 except for the poly-Si thin film. Thus, the samereference numerals will be used to refer to the same or like parts asthose described in FIGS. 1 to 8 and any further explanation concerningthe above elements will be omitted.

Referring to FIG. 11, a laser unit that generates a laser beam 200 isprepared on an a-Si thin film 130 that is formed on a substrate 100. Thesubstrate 100 is positioned on an XY-stage 20. The XY-stage 20transports and rotates the substrate 100. The laser beam 200 has a beamshape such as an elliptical shape, a quadrangular shape, etc. A firstwidth of the beam shape of the laser beam 200 is shorter than a secondwidth of the beam shape of the laser beam 200. The second width of thebeam shape of the laser beam 200 is controlled by an optical controller(not shown) of the laser unit 10 shown in FIG. 1.

The substrate 100 includes a first end portion 102 that is adjacent to aleft side of the substrate 100, a second end portion 104 that isadjacent to a right side of the substrate 100, a third end portion 106that is adjacent to an upper side of the substrate 100, and a fourth endportion 108 that is adjacent to a lower side of the substrate 100, asviewed from the perspective shown in FIG. 11. The laser beam 200includes a first laser beam 200 a and a second laser beam 200 b. Thesecond width of the beam shape of the first laser beam 200 a issubstantially equal to a side length of each of the first and second endportions 102 and 104. The second width of the beam shape of the secondlaser beam 200 b is substantially equal to a side length of each of thethird and fourth end portions 106 and 108.

The first laser beam 200 a generated from the laser unit is irradiatedonto a portion of the a-Si thin film adjacent to the first end portion102 of the substrate to liquefy the portion of the a-Si thin film toform the liquefied silicon region. The portion of the a-Si thin filmonto which the first laser beam 200 a is irradiated is fully liquefied.That is, a phase of the a-Si thin film is changed from an amorphoussolid phase to a liquid phase.

The liquefied silicon region is crystallized from sides of the liquefiedsilicon region through a solid phase crystallization. That is, theremaining portion of the a-Si functions as the core of the crystalgrowth so that the liquefied silicon region is crystallized frominterfaces between the remaining portion of the a-Si and the liquefiedsilicon region to a center of the liquefied silicon region by a lateralgrowth. When the first crystallization of the liquefied silicon regionis completed, a protruding portion is formed in the center of thecrystallized poly-Si.

The laser unit is repetitively shifted by an interval from the first endportion 102 toward the second end portion 104, and the first laser beam200 a generated from the laser unit is repetitively irradiated onto aportion of the a-Si thin film, a portion of the crystallized poly-Si andthe protruding portion to fully liquefy the portion of the a-Si thinfilm, the portion of the crystallized poly-Si and the protruding portionto form the liquefied silicon region, and eliminate the protrudingportion. In FIG. 11, the interval of the first laser beam 200 a is lessthan a half of a first width of the beam shape of the first laser beam200 a. The crystallized poly-Si forms first silicon grains, and thefirst silicon grains grow to form a first poly-Si thin film. The firstpoly-Si thin film includes the first silicon grains and the firstsilicon grain boundaries. The first silicon grains and the first silicongrain boundaries extend in a first direction.

When the first poly-Si thin film is completed, the XY-stage 20 isrotated by about ninety degrees so that the substrate 100 is rotated byabout ninety degrees. The second width of the beam shape of the laserbeam 200 is changed from the length of each of the first and second endportions 102 and 104 to the length of each of the third and fourth endportions 106 and 108. That is, the first laser beam 200 a is changedinto the second laser beam 200 b.

The second laser beam 200 b generated from the laser unit is irradiatedonto a portion of the first poly-Si thin film adjacent to the third endportion 106 of the substrate 100 to fully liquefy the portion of thefirst poly-Si thin film to form the liquefied silicon region.Alternatively, the first poly-Si thin film may be partially melted toform a partially liquefied silicon region. The liquefied silicon regionis then crystallized through the solid phase crystallization, and aprotruding portion that extending in the first direction is formed. Thelaser unit is repetitively shifted by an interval from the third endportion 106 toward the fourth end portion 108, and the second laser beam200 b generated from the laser unit is repetitively irradiated onto aportion of the first poly-Si thin film, a portion of the crystallizedpoly-Si and a protruding portion to fully liquefy the portion of thea-Si thin film, the portion of the crystallized poly-Si and theprotruding portion to form the liquefied silicon region, and eliminatethe protruding portion. In FIG. 11, the interval of the second laserbeam 200 b is more than a half of a first width of the beam shape of thesecond laser beam 200 b. The interval of the second laser beam 200 b maybe substantially equal to the interval of the first laser beam 200 a.

The crystallized poly-Si forms second silicon grains, and the secondsilicon grains grow to form a second poly-Si thin film. The secondpoly-Si thin film includes the second silicon grains and second silicongrain boundaries. In FIG. 11, the second silicon grains are formed by agrowth of the first silicon grains in the first direction so that thesecond silicon grains have a larger size than the first silicon grains.

FIGS. 12A to 12C are plan views showing the method shown in FIG. 11.

Referring to FIG. 12A, the first laser beam 200 a is repetitivelyirradiated onto the a-Si thin film, and shifted by an interval from thefirst end portion 102 toward the second end portion 104 so that thefirst poly-Si thin film 140 without protruding portions is formed. Thefirst poly-Si thin film 140 includes the first silicon grains 143 andthe first silicon grain boundaries 144 that extend in the firstdirection.

Referring to FIG. 12B, in order to grow the first silicon grains 143 inthe second direction, the second laser beam 200 b generated from thelaser unit is irradiated onto a portion of the first poly-Si thin film140 adjacent to the third end portion 106 of the substrate 100 to fullyliquefy the portion of the first poly-Si thin film 140, thus forming theliquefied silicon region. Alternatively, the portion of the firstpoly-Si thin film 140 onto which the second laser beam 200 b isirradiated may be partially liquefied to form a partially liquefiedsilicon region. The first silicon grain boundaries 144 are eliminated bythe liquefaction. Therefore, the first silicon grains 143 grow in thesecond direction to form the second silicon grains 162.

Referring to FIG. 12C, the laser unit is repetitively shifted by aninterval ‘I’ from the third end portion 106 toward the fourth endportion 108, and the second laser beam 200 b generated from the laserunit is repetitively irradiated onto the portion of the first poly-Sithin film 140 so that the first silicon grains 143 repetitively grow ina second direction with respect to the substrate. Therefore, the secondsilicon grains 162 have greater size than the first silicon grains 143.Alternatively, the second silicon grains 162 may be pseudomono-crystalline grains.

FIG. 13 is a plan view showing the poly-Si thin film formed by themethod shown in FIG. 11.

Referring to FIG. 13, the second poly-Si thin film 160 includes thesecond silicon grains 162 and second silicon grain boundaries 164. Eachof the second silicon grains 162 extends in the first and seconddirections. The second silicon grain boundaries 164 are positionedbetween adjacent second silicon grains 162. In FIG. 13, the secondsilicon grain boundaries 164 have a roughly circular shape. As the sizeof the second silicon grains 162 is increased, the electrical mobilityof the second poly-Si thin film 160 is also increased.

In addition, as the size of the second silicon grains 162 is increased,a density of the silicon grain boundaries 164 is decreased to decrease aleakage current that may be formed through the silicon grain boundaries164 when a TFT is turned off.

The substrate 100 is rotated by the ninety degrees, and the first andsecond laser beams 200 are irradiated onto the a-Si thin film 130 in thefirst and second directions to maximize the size of the second poly-Sigrains 162, thereby increasing the electrical mobility.

FIGS. 14A to 14D are cross-sectional views showing a method ofmanufacturing a poly-Si thin film in accordance with one embodiment. Inparticular, FIG. 14A is a cross-sectional view showing a poly-Si patternon a transparent substrate.

Referring to FIG. 14 a, an oxide layer 320 is formed on a transparentsubstrate 310. An a-Si thin film is formed on the oxide layer 320.

The a-Si thin film is converted into a poly-Si thin film using a laserbeam. In particular, a laser unit that generates the laser beam isprepared on the transparent substrate 310 having the a-Si thin film. Thelaser beam has a beam shape such as an elliptical shape, a quadrangularshape, etc. A second width of the beam shape of the laser beam isgreater than a first width of the beam shape of the laser beam. Thelaser beam is irradiated onto a portion of the a-Si thin film adjacentto a first end portion of the transparent substrate 310 to fully liquefya portion of the a-Si thin film. Alternatively, the portion of the a-Sithin film adjacent to a first end portion of the transparent substrate310 may be partially liquefied. Silicon grains grow in the liquefiedsilicon region through a solid phase crystallization. The laser beam isrepetitively irradiated onto the a-Si thin film, and shifted from thefirst end portion to a second end portion of the transparent substrate310 to form a poly-Si thin film.

The poly-Si thin film is partially etched through an etching processsuch as a plasma etching, a wet etching, etc., to form a poly-Si pattern330.

Referring to FIG. 14B, a first insulating layer 340 is formed on thepoly-Si pattern 330 to protect the poly-Si pattern 330. In FIG. 14B, thefirst insulating layer 340 is formed through a plasma enhanced chemicalvapor deposition (PECVD) process.

A gate electrode G is formed on the first insulating layer 340. In FIG.14B, the gate electrode G is positioned at the center of the poly-Sipattern 330. In particular, a metal is deposited on the first insulatinglayer 340, and partially etched to form the gate electrode G.

Referring to FIG. 14C, a second insulating layer 350 is formed on thegate electrode G and the first insulating layer 340. The secondinsulating layer 350 may be formed through a PECVD process. A thicknessof the second insulating layer 350 is more than a predeterminedthickness to improve credibility and reliability of the TFT 300 and toprevent a cross-talk. In FIG. 14C, the thickness of the secondinsulating layer 350 is more than about 6,000 Å.

The first and second insulating layers 340 and 350 are partially etchedto form a first contact hole 352 and a second contact hole 354. Thefirst contact hole 352 is adjacent to a right side of the gate electrodeG, and the second contact hole 354 is adjacent to a left side of thegate electrode G. The second contact hole 354 is spaced apart from thefirst contact hole 352.

Referring to FIG. 14D, a source electrode S and a drain electrode D areformed on the second insulating layer 350. The source electrode S iselectrically connected to the poly-Si pattern 340 through the firstcontact hole 352, and the drain electrode D is electrically connected tothe poly-Si pattern 340 through the second contact hole 354.

A protecting layer 360 is formed on the second insulating layer 350having the source electrode S and the drain electrode D. The protectinglayer 360 is partially etched to form a pixel contact hole 362. A pixelelectrode 370 is formed on the protecting layer 360. The pixel electrode370 is transparent. The pixel electrode 370 is electrically connected tothe drain electrode D through the pixel contact hole 362.

The poly-Si pattern 340 having high electrically mobility is formed bythe laser beam to improve electrical characteristics of the TFT 300.

The TFT 300 is a top gate type TFT. Alternatively, the TFT may be abottom gate type TFT that has a poly-Si pattern interposed between agate electrode and source/drain electrodes.

In accordance with the present invention, the laser beam is repetitivelyirradiated onto the substrate, and shifted from the first end portiontoward the second end portion to form a poly-Si thin film havingincreased grain size and improved electrical characteristics.

In addition, the interval of the shift of the laser unit is controlledto control a manufacturing time of the poly-Si thin film.

The laser unit may be rotated by about ninety degrees so that the laserbeam is firstly and secondly irradiated onto the a-Si thin film. Thesize of the silicon grains is maximized to increase the electricalmobility.

The poly-Si pattern has high electrical mobility so that the TFT hasimproved electrical characteristics.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one of ordinary skill in the art within thespirit and scope of the present invention as hereinafter claimed.

1. A method of manufacturing a polysilicon thin film comprising:irradiating a laser beam generated from a laser unit onto a firstportion of an amorphous silicon thin film to liquefy the first portionof the amorphous silicon thin film, the laser beam having a beam shapeincluding a first width substantially in parallel with a first directionand a second width substantially in parallel with a second directionsubstantially perpendicular to the first direction; transporting thesubstrate or the laser beam for shifting the laser beam in the firstdirection to form a first polysilicon thin film; rotating the substrateor the laser beam by a predetermined angle after forming the firstpolysilicon thin film; and transporting the substrate or the laser beamfor shifting the laser beam in the second direction to liquefy the firstpolysilicon thin film and to form a second polysilicon film.
 2. Themethod of claim 1, wherein the second width is greater than the firstwidth, the beam shape of the laser unit is substantially the same shapeas a shape of the laser beam irradiated onto the first portion.
 3. Themethod of claim 2, wherein the amorphous silicon thin film is formed onthe substrate and the second width of the beam is substantially same toa side of the substrate.
 4. The method of claim 3, wherein the firstwidth of the beam is about 3 um to about 10 um.
 5. The method of claim1, wherein the amorphous silicon thin film is formed on the substrateand the second width of the beam is substantially same to a side of thesubstrate.
 6. The method of claim 5, wherein the first width of the beamis about 3 um to about 10 um.
 7. The method of claim 1, the shifting ofthe laser beam in the first direction is discrete.
 8. The method ofclaim 7, the discretion interval is same to or less than half of thefirst width of the laser beam.
 9. The method of claim 7, the discretioninterval is bigger than half and less than the first with of the laserbeam.
 10. The method of claim 7, wherein the second width is greaterthan the first width, the beam shape of the laser unit is substantiallythe same shape as a shape of the laser beam irradiated onto the firstportion.
 11. The method of claim 10, wherein the amorphous silicon thinfilm is formed on the substrate and the second width of the beam issubstantially same to a side of the substrate.
 12. The method of claim11, wherein the first width of the beam is about 3 um to about 10 um.13. The method of claim 7, wherein the amorphous silicon thin film isformed on the substrate and the second width of the beam issubstantially same to a side of the substrate.
 14. The method of claim13, wherein the first width of the beam is about 3 um to about 10 um.15. A method of manufacturing a thin film transistor comprising: formingan amorphous silicon thin film on a substrate; irradiating a laser beamgenerated from a laser unit onto the amorphous silicon thin film tochange the amorphous silicon thin film into a polysilicon thin film;partially etching the polysilicon thin film to form a polysiliconpattern; forming a first insulating layer on the substrate having thepolysilicon pattern; forming a gate electrode on the first insulatinglayer overlapping a portion of the polysilicon pattern; forming a secondinsulating layer on the first insulating layer and the gate electrode;partially etching the first and second insulating layers to form contactholes; and forming a source electrode and a drain electrode on thesecond insulating layer, the source electrode being spaced apart fromthe drain electrode, the source and drain electrodes being electricallyconnected to the polysilicon pattern through the contact holes, whereinthe laser beam irradiation scans a first direction to change theamorphous silicon thin film into a first polysilicon thin film, and thelaser beam irradiation scans a second direction to change the firstpolysilicon thin film into a second polysilicon thin film.
 16. Themethod of claim 15, the first direction and the second direction aredifferent from each other.
 17. The method of claim 16, the firstdirection and the second direction are substantially perpendicular. 18.The method of claim 16, wherein the beam shape of the laser unit iselongated and substantially the same shape as a shape of the laser beamirradiated onto the first portion.
 19. The method of claim 18, whereinthe length of the beam is substantially same to a side of the substrate.20. The method of claim 19, wherein the width of the beam is about 3 umto about 10 um.
 21. The method of claim 16, the scanning of the laserbeam in the first direction is discrete.
 22. The method of claim 21, thediscretion interval is same to or less than half of the first width ofthe laser beam.
 23. The method of claim 21, the discretion interval isbigger than half and less than the first with of the laser beam.
 24. Themethod of claim 21, wherein the beam shape of the laser unit iselongated substantially the same shape as a shape of the laser beamirradiated onto the first portion.
 25. The method of claim 24, whereinthe length of the beam is substantially same to a side of the substrate.26. The method of claim 25, wherein the width of the beam is about 3 umto about 10 um.
 27. The method of claim 21, wherein the beam iselongated and the length of the beam is substantially same to a side ofthe substrate.
 28. The method of claim 27, wherein the width of the beamis about 3 um to about 10 um.
 29. A method of manufacturing apolysilicon thin film comprising: irradiating a laser beam generatedfrom a laser unit onto a first portion of an amorphous silicon thin filmto liquefy the first portion of the amorphous silicon thin film, thelaser beam having a beam shape including a first width substantially inparallel with a first direction and a second width substantially inparallel with a second direction substantially perpendicular to thefirst direction; transporting the substrate or the laser beam forscanning the laser beam in the first direction to form a firstpolysilicon thin film; rotating the substrate or the laser beam by apredetermined angle after forming the first polysilicon thin film; andtransporting the substrate or the laser beam for scanning the laser beamin the second direction to liquefy the first polysilicon thin film andto form a second polysilicon film.